The Community Earth System Model version 1.3 (CESM1.3) http://www2.cesm.ucar.edu See the CESM web site for documentation and information. For commits to the CESM svn repo 1) check out the latest ccsm4 tag but do not populate external directories > svn co --ignore-externals $SVNREPO/cesm1/tags/cesm1_3_alpha## my_sandbox > svn co -N $SVNREPO/cesm1/tags/cesm1_3_alpha## my_sandbox 2) modify the file SVN_EXTERNAL_DIRECTORIES with any changes to component tags > cd my_sandbox > emacs SVN_EXTERNAL_DIRECTORIES 3) set the property for the external definitions - don't forget the dot at the end > svn propset svn:externals -F SVN_EXTERNAL_DIRECTORIES . 4) populate your sandbox with the external files > svn update 5) test 6) document your mods > cp ChangeLog_template ChangeLog.new > cat ChangeLog >> ChangeLog.new > emacs ChangeLog.new > mv ChangeLog.new ChangeLog 7) copy your sandbox to a new tag in the repository > svn copy . $SVNREPO/ccsm4/tags/cesm1_3_alpha## -m "created tag cesm1_3_alpha##"